1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor substrate. More particularly, the present invention relates to a method of manufacturing an oxygen ion-implanted—etch/polish stop bonded substrate affording improved SiO2/Si interface roughness by using a wafer with a substrate resistivity of 1 to 100 mΩcm as a wafer on the active layer side. The manufacturing method of the present invention can be applied to both silicon-on-insulator (SOI) and direct silicon bonding (DSB) substrates.
2. Discussion of the Background
In contrast to conventional silicon wafers, SOI wafers provide superior features, such as device isolation, reduced parasitic capacitance between device and substrate, and the ability to form three-dimensional structures. Thus, they are employed in high-speed, low power consumption LSIs (“large-scale integration”). Methods of manufacturing SOI wafers by bonding, in which two silicon wafers on which oxide films have been formed are bonded together and a SOI layer (active layer) is then bonded by grinding and polishing, are known. The Smart Cut method (registered trademark) is included among these bonding methods (see Japanese Unexamined Patent Publication (KOKAI) Heisei No. 9-116125 or English language family member U.S. Pat. No. 6,372,609, Japanese Unexamined Patent Publication (KOKAI) No. 2000-124092 or English language family member U.S. Pat. No. 5,998,281, which are expressly incorporated herein by reference in their entirety).
In SOI wafers, thinning of the SOI layer (active layer) and uniform film thickness are desirable. Thus, a new method for such purposes has been developed. In this new method, an active layer wafer having an oxygen ion implantation layer and a base layer wafer are bonded together, the oxygen ion implantation layer is converted to a SiO2 layer by heat treatment, grinding and polishing are conducted from the active layer wafer side through to the SiO2 layer, and the SiO2 layer is removed to obtain a wafer with a thin SOI layer (active layer) of uniform film thickness. WO 2005/074033 A1 or English language family member US2007/0161199 A1, which are expressly incorporated herein by reference in their entirety, discloses the aforementioned method. The oxygen ion implantation layer functions as a polish stop layer.
In recent years, device miniaturization and the reduction of power consumption have resulted in a thinning of the BOX oxide film. Further, directly bonded DSB substrates have been developed in which bonding is conducted without a BOX (oxide film), for example. When directly bonding without an oxide film, the wafers are bonded after conducting the usual cleaning (SC1).
However, the bonding method employing the polish stop layer described in WO 2005/074033 A1 presents the following problems:
(1) There is substantial roughness at the interface between the silicon substrate and the layer containing SiO2 phase particles or the continuous SiO2 layer serving as the polish stop layer, resulting in great roughness of the outer surface of the bonded wafer that is a final product;
(2) Thus, after fabricating the SOI structure, it becomes necessary to conduct additional processing in the form of polishing or a high-temperature heat treatment at 1,100° C. for one hour to improve surface roughness; and
(3) Problems relating to quality caused by deterioration of in-plane uniformity of the top layer (active layer) due to the additional processing.
The same problems as in (1) occur in bonding methods employing a polish stop layer, both in SOI substrates and DSB substrates.